This invention relates to manual transmission lubricants which are thermally and oxidatively stable and are effective even at long drain intervals. More specifically, the invention relates to manual transmission lubricants with a metal thiophosphate, a phosphite and a basic salt of an acidic organic compound which provide thermal and oxidation protection to the manual transmission lubricants.
Manual transmissions pose problems for lubricant formulators because of the configuration of the transmission and the metallurgy of the transmission components. The manual transmission uses spur gears which provided pressure and shearing in essentially linear force lines. In other words, the force of shear has only one directional component. This is in contrast to gears used for the driveline which are hypoid gears. In a hypoid gear, the gears mesh in such a way that the shearing force has two directional components"". A linear component and a second transverse component across the gear face. The level of extreme pressure protection needed for a manual transmission is lower than that needed for a hypoid gear assembly.
The manual transmission requires certain frictional properties from the lubricant to provide the ability of the manual transmission to perform gear changes. For the gear to be changed, the transmission must bring the drive shaft and the gear into position for meshing. The meshing is accomplished by a synchronizer when the synchronizing parts (plate to plate or ring to cone) are reduced to relative zero velocity. If these parts do not obtain zero relative velocity, then a phenomenon known as synchronizer clashing (sometimes referred to as crashing) occurs. Clashing of the synchronizer results when the dynamic coefficient of friction building between the engaging synchronizer parts (plate to plate or ring to cone) falls below a critical minimum value. Below this critical minimum value the synchronizer parts do not attain zero relative velocity and the lockup mechanism (e.g., spline camphers) contacts the rotating member (e.g., cone camphers) resulting in a loud noise (clashing/crashing).
The components of the manual transmission are typically bronze or brass. These metals are susceptible to corrosion and chemical attack from typical antiwear and extreme pressure agents which contain sulfur, particularly active sulfur. For instance, organic polysulfides which are typically used with lubricants for hypoid gears cause damage to the manual transmission synchronizer components.
Previously, manual transmission lubricants would use metal thiophosphonates or antiwear agents. These metal salts were typically barium salts. The accumulation of heavy metals, such as barium, in the environment has lead to the desire to eliminate the use of heavy metal salts in manual transmission lubricants.
It is desirable to provide lubricants which can provide the antiwear protection and viscosity protection for manual transmissions without harming the components of the transmission. It is desirable that the lubricants be free of barium salts.
This invention relates to a manual transmission lubricants comprising a major amount of an oil of lubricating viscosity, (A) at least one metal thiophosphate, (B) at least one phosphite, and (C) at least one basic salt of an acidic organic compound. In another embodiment, the manual transmission further comprises at least metal salt of a phenol. The lubricants provide the antiwear and extreme pressure protection needed for the manual transmission without harming the manual transmission components.
The term xe2x80x9chydrocarbylxe2x80x9d includes hydrocarbon as well as substantially hydrocarbon groups. Substantially hydrocarbon describes groups which contain heteroatom substituents that do not alter the predominantly hydrocarbon nature of the substituent. Examples of hydrocarbyl groups include the following:
(1) hydrocarbon substituents, i.e., aliphatic (e.g., alkyl or alkenyl) and alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, aromatic-, aliphatic- and alicyclic-substituted aromatic substituents and the like as well as cyclic substituents wherein the ring is completed through another portion of the molecule (that is, for example, any two indicated substituents may together form an alicyclic radical);
(2) substituted hydrocarbon substituents, i.e., those substituents containing non-hydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon nature of the substituent; those skilled in the art will be aware of such groups (e.g., halo (especially chloro and fluoro), hydroxy, mercapto, nitro, nitroso, sulfoxy, etc.);
(3) heteroatom substituents, i.e., substituents which will, while having a predominantly hydrocarbon character within the context of this invention, contain an atom other than carbon present in a ring or chain otherwise composed of carbon atoms (e.g., alkoxy or alkylthio). Suitable heteroatoms will be apparent to those of ordinary skill in the art and include, for example, sulfur, oxygen, nitrogen and such substituents as, e.g. parietal, furyl, thienyl, imidazolyl, etc.
In general, no more than about 2, preferably no more than one heteroatom substituent will be present for every ten carbon atoms in the hydrocarbyl group. Typically, there will be no such heteroatom substituents in the hydrocarbyl group. Therefore, the hydrocarbyl group is purely hydrocarbon.
As described above the lubricating compositions comprise (A) at least one metal thiophosphate, (B) at least one hydrocarbyl phosphite, and (C) at least one overbased salt of an acidic organic compound. These lubricants provide thermal and oxidative protection as well at antiwear and extreme pressure protection to machinery.
Metal Thiophosphates
The manual transmission lubricants, and concentrates include at least one metal thiophosphate. Typically, the metal thiophosphate is present at a level from about 0.1% to about 5%, or from about 0.3% or to about 4%, or from about 0.5% to about 3%, or from 0.7% to about 2% by weight in the lubricating composition. Here and elsewhere in the specification and claims, the range and ratio limits may be combined.
The metal thiophosphates include mono and dithiophosphates as well as mixtures of mono and dithiophosphates. The mixtures may be formed in situ reaction or may be formed by blending a metal monothiophosphate with a metal dithiophosphate. The monothiophosphates or mixtures of mono and dithiophosphates may also be formed through reacting a metal dithiophosphate with steam. Alternatively, the monothiophosphate may be prepared by reacting one or more of the phosphites discussed herein with a sulfur or a sulfur compound.
In one embodiment, the metal thiophosphate is represented by the formula 
wherein where X1 and X2 are independently oxygen or sulfur provided that one of these is sulfur, R3 and R4 are each independently hydrocarbyl groups containing from 3 to about 13 carbon atoms, preferably from 3 to about 8, M is a metal, and z is an integer equal to the valence of M. Preferably both X1 and X2 are sulfur.
The hydrocarbyl groups R3 and R4 in the thiophosphate may be alkyl, cycloalkyl, aralkyl or alkaryl groups. Illustrative alkyl groups include isopropyl, isobutyl, n-butyl, sec-butyl, the various amyl groups, n-hexyl, methylisobutyl carbinyl, heptyl, 2-ethylhexyl, diisobutyl, isooctyl, nonyl, behenyl, decyl, dodecyl, tridecyl, etc. Illustrative lower alkylphenyl groups include butylphenyl, amylphenyl, heptylphenyl, etc. Cycloalkyl groups likewise are useful and these include chiefly cyclohexyl and the lower alkylkyclohexyl radicals. Many substituted hydrocarbon groups may also be used, e.g., chloropentyl, di-chlorophenyl, and dichlorodecyl.
The thiophosphoric acids from which the metal salts useful in this invention are prepared are well known. Examples of dihydrocarbyl dithiophosphoric acids and metal salts, and processes for preparing such acids and salts are found in, for example, U.S. Pat. Nos. 4,263,150; 4,289,635; 4,308,154; and 4,417,990. These patents are hereby incorporated by reference for such disclosures.
The thiophosphoric acids are prepared by the reaction of a phosphorus sulfide with an alcohol or phenol or mixtures of alcohols. Useful phosphorus sulfide-containing sources include phosphorus pentasulfide, phosphorus sesquisulfide, phosphorus heptasulfide and the like. The reaction involves four moles of the alcohol or phenol per mole of phosphorus pentasulfide, and may be carried out within the temperature range from about 50xc2x0 C. to about 200xc2x0 C. Thus the preparation of O,O-di-n-hexyl dithiophosphoric acid involves the reaction of phosphorus pentasulfide with four moles of n-hexyl alcohol at about 100xc2x0 C. for about two hours. Hydrogen sulfide is liberated and the residue is the defined acid. The preparation of the metal salt of this acid may be effected by reaction with metal oxide. Simply mixing and heating these two reactants is sufficient to cause the reaction to take place and the resulting product is sufficiently pure for the purposes of this invention.
The metal salts of dihydrocarbyl dithiophosphates which are useful in this invention include those salts containing Group I metals, Group II metals, aluminum, lead, tin, molybdenum, manganese, cobalt, and nickel. Group I and Group II (including Ia, Ib, IIa and IIb) are defined in the Periodic Table of the Elements in the Merck Index, 9th Edition (1976). The Group II metals, aluminum, tin, iron, cobalt, lead, molybdenum, manganese, nickel and copper are among the preferred metals. Zinc and copper are especially useful metals. In one embodiment, the lubricating compositions contain a zinc dihydrocarbyl dithiophosphate and a copper dihydrocarbyl dithiophosphate. Examples of metal compounds which may be reacted with the acid include lithium oxide, lithium hydroxide, sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, silver oxide, magnesium oxide, magnesium hydroxide, calcium oxide, zinc hydroxide, strontium hydroxide, cadmium oxide, cadmium hydroxide, barium oxide, aluminum oxide, iron carbonate, copper hydroxide, copper oxide, lead hydroxide, tin butylate, cobalt hydroxide, nickel hydroxide, nickel carbonate, zinc oxide, etc.
In some instances, the incorporation of certain ingredients such as small amounts of the metal acetate or acetic acid in conjunction with the metal reactant will facilitate the reaction and result in an improved product. For example, the use of up to about 5% of zinc acetate in combination with the required amount of zinc oxide facilitates the formation of a zinc dithiophosphate.
In one preferred embodiment, the alkyl groups R3 and R4 are derived from secondary alcohols such as isopropyl alcohol, secondary butyl alcohol, 2-pentanol, 2-methyl4-pentanol, 2-hexanol, 3-hexanol, isooctyl etc.
Especially useful metal dithiophosphates can be prepared from dithiophosphoric acids which in turn are prepared by the reaction of phosphorus pentasulfide with mixtures of alcohols. In addition, the use of such mixtures enables the utilization of cheaper alcohols which in themselves may not yield oil-soluble dithiophosphoric acids or salts thereof. Thus a mixture of isopropyl and hexyl alcohols can be used to produce a very effective, oil-soluble metal dithiophosphate. For the same reason mixtures of dithiophosphoric acids can be reacted with the metal compounds to form less expensive, oil-soluble salts.
The mixtures of alcohols may be mixtures of different primary alcohols, mixtures of different secondary alcohols or mixtures of primary and secondary alcohols. Examples of useful mixtures include: n-butanol and n-octanol; n-pentanol and 2-ethyl-1-hexanol; isobutanol and n-hexanol; isobutanol and isoamyl alcohol; isopropanol and 2-methyl4-pentanol; isopropanol and sec-butyl alcohol; isopropanol and isooctyl alcohol; etc.
The following examples illustrate the preparation of metal dithiophosphates.